A phase locked system is employed to inhibit the effect of disturbance on the interferometric fiber sensors(IFS).The phase locked system is analyzed based on automatic control technology.The theoretical analysis shows that two integrity components are necessary to achieve the best phase-lock effect.The experimental results show that the phase locked system could inhibit the disturbance effectively,and consist with the theoretical analysis.Furthermore,a practical phase locked 2-order system is demonstrated and its output variance is about 3.5 mV while that of the 1-order system is 31 mV.The stability of the system has been improved by 1 order of magnitude.